fn: fix UnwrapOrFail semantics

fn/option.go

@@ -1,6 +1,10 @@
 package fn
 
-import "testing"
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
 
 // Option[A] represents a value which may or may not be there. This is very
 // often preferable to nil-able pointers.
@@ -61,14 +65,9 @@ func (o Option[A]) UnwrapOrFunc(f func() A) A {
 func (o Option[A]) UnwrapOrFail(t *testing.T) A {
 	t.Helper()
 
-	if o.isSome {
-		return o.some
-	}
+	require.True(t, o.isSome, "Option[%T] was None()", o.some)
 
-	t.Fatalf("Option[%T] was None()", o.some)
-
-	var zero A
-	return zero
+	return o.some
 }
 
 // UnwrapOrErr is used to extract a value from an option, if the option is

fn/option_test.go

@@ -0,0 +1,11 @@
+package fn
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestOptionUnwrapOrFail(t *testing.T) {
+	require.Equal(t, Some(1).UnwrapOrFail(t), 1)
+}

fn/result.go

@@ -3,6 +3,8 @@ package fn
 import (
 	"fmt"
 	"testing"
+
+	"github.com/stretchr/testify/require"
 )
 
 // Result represents a value that can either be a success (T) or an error.
@@ -114,13 +116,11 @@ func (r Result[T]) UnwrapOrElse(f func() T) T {
 func (r Result[T]) UnwrapOrFail(t *testing.T) T {
 	t.Helper()
 
-	if r.IsErr() {
-		t.Fatalf("Result[%T] contained error: %v", r.left, r.right)
-	}
+	require.True(
+		t, r.IsOk(), "Result[%T] contained error: %v", r.left, r.right,
+	)
 
-	var zero T
-
-	return zero
+	return r.left
 }
 
 // FlatMap applies a function that returns a Result to the success value if it

fn/result_test.go

@@ -0,0 +1,11 @@
+package fn
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestResultUnwrapOrFail(t *testing.T) {
+	require.Equal(t, Ok(1).UnwrapOrFail(t), 1)
+}